Performance degradation of an LC-tank VCO by impact of digital switching noise

Abstract

In mixed-signal designs, digital switching noise is an important limitation for the analog and RF performance. This paper reports a thorough experimental and analytical study of the impact of digital switching noise on a 3.5 GHz LC-tank voltage controlled oscillator (VCO) in 0.18 /spl mu/m CMOS. Frequency modulation is recognized as the dominating mechanism behind the impact of digital switching noise in the investigated frequency range (DC to 15 MHz). The dominating coupling path, from the source of noise to the VCO, in this frequency range is via the non-ideal metal ground lines.